1. Field of the Invention
This invention relates to high powered density welding and more particularly to a manual keyhole welding process for eliminating defects in weldable material.
2. Description of the Related Art
Typically, during the manufacturing of large aluminum and other weldable structures automatic welding techniques are utilized to form the basic structure. Manual welding techniques are later used to repair undesirable defects generated during the automated welding process. The defects are usually detected by X-ray techniques or visual inspection and removed by mechanical means such as grinding or machining. The structure is then re-melted or repair welded using gas tungsten arc welding (GTAW) or plasma arc welding techniques.
GTAW produces an arc between a non-consumable electrode and the workpiece, in an inert gas atmosphere. A gas discharge is formed as a result of the ionization of the gas. GTAW is generally conducted in a power density range of between approximately 5.times.10.sup.6 W/mm.sup.2 and 5.times.10.sup.8 W/mm.sup.2 to provide melting of the workpiece. Plasma arc welding techniques involve gas discharged through a constricted orifice resulting in a collimated, high velocity, high temperature discharge. Plasma arc welding is generally conducted in a power density range of between 5.times.10.sup.8 W/mm.sup.2 and 3.times.10.sup.10 W/mm.sup.2.
At levels greater than about 1.times.10.sup.10 W/mm.sup.2 the power density is sufficiently high during the plasma arc welding to not only merely melt but also to completely penetrate the structure to form a hole or "keyhole", as it is commonly called. This technique is described in the book entitled "Physics of Welding", Chapter 8, High Power Density Welding. Keyhole welding provides deep, narrow penetration as compared to the GTAW process.
U.S. Pat. No. 4,628,177, entitled "Arc Welding Torch", issued to W. R. Dempsey et al discloses a sealless plasma arc welding torch which uses a power source having a square time-based control wave form. Dempsey used a shield gas which may be helium.